oi;k;[N' of volcanic hocks discuhsed. 13 



but if \'ou will go to siK'li or such a locality, — inflicatin<^ some new one, — 

 you will find an undoubted passage of tli(; sedimentary rock into eruptive 

 forms." When this new locality is also examined and the statements are 

 found to be erroneous, another one is mentioned, and so on ; until one must 

 demand hereafter of these observers that they shall select some locality on 

 which they shall be willing to fully and finally stake their pet hypothesis, 

 and abide by the evidence. 



It has been claimed that the results of chemical analysis show that vol- 

 canic rocks are derived from sedimentary ones. While it is true that the 

 former have a composition chemically like some of the latter, this resem- 

 blance is easily explained by the fact that a sedimentary rock ought to 

 resemble chemically the massive rock from whose destruction it came. The 

 chief difference between them would be that resulting from the change 

 brought about by outside inOuences, the introduction of foreign material, 

 etc. Hence the chemical resemblance between the two classes of rocks 

 can naturally and readily be explained by the derivation of the sedimentary 

 from the eruptive rocks; and there is no need to resort to the unnntural and 

 hypothetical derivation of the volcanic from the sedimentary rocks. The 

 former derivation is the one seen to take place every day, while the latter 

 is unproved as yet, and those who hold it are apparently looking at the 

 effect, and making it the cause. In other words, it seems to the writer that 

 these observers have taken hold of the subject at the wrong end. 



In examining the products of volcanoes, certain minerals appear to be 

 characteristic of them, which are of prior origin to the consolidation of the 

 lava. These minerals show evidence that a hot magma has directly acted 

 upon them, and every gradation can frequently be seen between the almost 

 mitouched mineral, and the nearly destroyed one. 



I regard these minerals, unless they were caught up by the lava during 

 its passage from the earth's interior to its surface, as evidences tint the 

 material from which the lava was derived is no longer in its original con- 

 dition, although this condition was not like that of any of our sedimentary 

 rocks. Certain of these minerals are easily destroyed ; two at least, sulYer- 

 ing alteration readily on exposure, and it seems impossible that they could 

 survive when the much less perishable materials of our sedimentary rocks 

 have been entirely obliterated, if, as is supposed by many, they were ever 

 there. These minerals are unlike, either in species, variety, or form, with 

 possibly a few exceptions, any minerals occurring in sedimentary rocks as a 



